Perpendicular magnetic recording medium and method of manufacturing the same and product thereof

Abstract

The quantity of oxide contained in a magnetic layer is controlled to control the crystal grains and the segregation structure for ensuring low noise characteristic in a granular magnetic layer of a perpendicular magnetic recording medium. The granular magnetic layer consists of ferromagnetic crystal grains and a nonmagnetic grain boundary region mainly of an oxide surrounding the ferromagnetic crystal grains. The perpendicular magnetic recording medium has a nonmagnetic underlayer composed of a metal or alloy having hexagonal closest-packed crystal structure. The ferromagnetic crystal grain is composed of an alloy containing at least cobalt and platinum. The volume proportion of the nonmagnetic grain boundary region mainly of the oxide falls within a range of 15% to 40% of the volume of the total magnetic layer.

1. A perpendicular magnetic recording medium comprising:
 a nonmagnetic substrate; and 
 at least a seed layer, a nonmagnetic underlayer, a magnetic layer, and a protective film sequentially laminated on the substrate, 
 wherein the seed layer is composed of a metal or alloy containing a face centered cubic (fcc) crystal structure selected from at least one element of Ni, Cu, Au, Pd, Pt, and Ir, 
 wherein the nonmagnetic underlayer is composed of a metal or alloy having a hexagonal closest-packed (hcp) crystal structure, 
 wherein the magnetic layer consists essentially of ferromagnetic crystal grains and a nonmagnetic grain boundary region, the nonmagnetic grain boundary region being composed of an oxide surrounding the ferromagnetic crystal grains, 
 wherein the ferromagnetic crystal grains are composed of an alloy containing at least cobalt and platinum, and 
 wherein a volume occupied by the grain boundary region falls within a range of 15% to 40% of a total volume of the magnetic layer, and a coercive force (Hc) thereof is greater than 3000 Oe and no higher than about 3700 Oe. 
 
     
     
       2. A perpendicular magnetic recording medium according to  claim 1 , wherein the magnetic layer has a thickness falling within a range of 5 nm to 20 nm. 
     
     
       3. A perpendicular magnetic recording medium according to  claim 1 , wherein the substrate is composed of a plastic resin. 
     
     
       4. A perpendicular magnetic recording medium according to  claim 2 , wherein the substrate is composed of a plastic resin. 
     
     
       5. A method of manufacturing a perpendicular magnetic recording medium, comprising steps of:
 depositing a seed layer is composed of a metal or alloy containing a face centered cubic (fcc) crystal structure selected from at least one element of Ni, Cu, Au, Pd, Pt, and Ir on a nonmagnetic substrate; 
 depositing a nonmagnetic underlayer composed of a metal or an alloy having a hexagonal closest-packed (hcp) crystal structure on the seed layer; 
 depositing a magnetic layer consisting essentially of ferromagnetic crystal grains and a nonmagnetic grain boundary region surrounding the ferromagnetic crystal grains by RF magnetron sputtering using a composite target containing a ferromagnetic alloy and an oxide on the underlayer, 
 wherein the ferromagnetic crystal grains are composed of an alloy containing at least cobalt and platinum, and 
 wherein a volume of the grain boundary region falls within a range of 15% to 40% of a total volume of the magnetic layer, and a coercive force (Hc) thereof is greater than 3000 Oe and no higher than about 3700 Oe; and 
 depositing a protective film on the magnetic layer. 
 
     
     
       6. A method of manufacturing a perpendicular magnetic recording medium according to  claim 5 , wherein the depositing steps of the seed layer, the nonmagnetic underlayer, the magnetic layer, and the protective film are performed without preheating the substrate. 
     
     
       7. A method for manufacturing a perpendicular magnetic recording medium according to  claim 6 , wherein a volume occupied by the oxide contained in the composite target falls within a range of 20% to 35% of a total volume of the target. 
     
     
       8. A method for manufacturing a perpendicular magnetic recording medium according to  claim 6 , wherein a volume occupied by the oxide contained in the composite target falls within a range of 20% to 35% of a total volume of the target. 
     
     
       9. A perpendicular magnetic recording medium according to  claim 1 , wherein the oxide In the magnetic layer is SiO 2 . 
     
     
       10. A method for manufacturing a perpendicular magnetic recording medium according to  claim 5 , wherein the oxide in the magnetic layer is SiO 2 . 
     
     
       11. A method for manufacturing a perpendicular magnetic recording medium according to  claim 7 , wherein the oxide in the magnetic layer is SiO 2 . 
     
     
       12. A method for manufacturing a perpendicular magnetic recording medium according to  claim 8 , wherein the oxide in the magnetic layer is SiO 2 .